Ozone is useful for numerous applications that require a high level of oxidation. For example, ozone is useful for disinfection of drinking water and has been used for water treatment since the early 1900's. More recently, ozone has been used for semiconductor device processing. One application for ozone in semiconductor device processing is forming insulating layers on semiconductor wafers by growing insulating films or by oxidizing thin films on the wafer, for example, high deposition rate chemical vapor deposition of high quality SiO2 can be accomplished by using a TEOS/ozone processor.
Another application for ozone in semiconductor device processing is for cleaning semiconductor wafers and equipment. Ozone is particularly useful for removing hydrocarbons from the surface of semiconductor wavers or from processing chambers. Using ozone for cleaning is advantageous because it avoids the use of dangerous chemicals, which require costly disposal. In contrast, ozone does not present a toxic waste disposal problem because ozone decays to oxygen without residues.
An ozone generator includes one or more individual ozone generating units, also referred to herein as ozone-producing cells. Each ozone-producing cell typically includes opposing electrode plates and a dielectric barrier. The dielectric barrier can be positioned against one of the electrode plates, forming a channel between the dielectric barrier and the opposing electrode plate. In operation, oxygen (O2) is provided to the cell and allowed to pass through the channel, whereupon it is acted upon by an electrical discharge between the electrode plates causing the dissolution and recombination of at least a portion of the oxygen atoms into ozone (O3) molecules.
To cause the electrical discharge or flux (i.e., ignite a plasma), high voltage AC power is applied across the opposing electrode plates of each ozone-producing cell. It has been determined that applying an AC load voltage of about 8 kilovolts, peak-to-peak at a relatively high frequency of between about 30 kHz and about 40 kHz is preferred for operation of at least some such ozone-producing cells. Since most applications derive such cell driving voltages from facility prime power, the ozone cell power system necessarily increases or otherwise steps up the voltage level from a facility power level (e.g., 208 volt AC, or 480 volt AC three-phase power). Additionally, the power system necessarily increases the frequency from a relatively low value of the facility supplied power (e.g., 50/60 Hz) to a relatively high value of the preferred frequency of operation.
The ozone-producing cell can be modeled as a capacitor in parallel with a series combination of a resistor and a bi-polar transient voltage suppressor. Application of electrical power can be hampered by the relatively large reactive load impedance resulting from the capacitor of the ozone cell. Electrical loads having such large reactive components tend to result in substantial heat loss and otherwise stress components of the power supply. Such components operate at increased power levels necessary to deliver suitable usable power (i.e., not reactive) to the load.